ch 2 single-gene inheritance Flashcards
chromatin
the substance of chromosomes
- now known to include DNA and chromosomal proteins
histone
a type of basic protein that forms the unit around which DNA is coiled in the nucleosomes of eukaryotic chromosomes
- H1 histone - make sure the nucleosomes get lined up correctly
nucleosome
the basic unit of eukaryotic chromosome structure; a ball of eight histone molecules that is wrapped by two coils of DNA
- associate with and coil around H1 histone
telomere
chromosome end
centromere
area of constriction
nucleolar organizer
tandem repeats of rRNA genes
heterochromatin
dense chromatin
- will appear darker with stain, more constricted
euchromatin
less dense chromatin
true-breeding
genotype is homozygous
dominant phenotype
the parental phenotype that is expressed in a heterozygote
dominant allele
an allele that expresses its phenotypic effect even when heterozygous with a recessive allele
- is A is dominant over a, then A/A and A/a have the same phenotype
recessive phenotype
the parental phenotype that is not expressed in the heterozygote
recessive allele
an allele whose phenotypic effect is not expressed in a heterozygote
first filial generation (f1)
the first generation resulting from a controlled cross between two known parents
second filial generation (F2)
the second generation resulting from a controlled cross between two known parents, generated by selfing/intercrossing the F1 generation
product rule
the probability of two independent events occurring simultaneously is the product of their individual probabilities
sum rule
the probability that one or the other of two mutually exclusive events will occur is the sum of the individual probabilities
Mendel’s law of equal segregation
two members of a gene pair segregate equally into the gametes, so that half the gametes carry one allele and the other half of gametes carry the other allele
-each parent contributes 1 copy of each factor to offspring with equal frequency
- gametes are haploid, fuse to form diploid offspring
test cross
a cross of an individual organism of unknown genotype or a heterozygote with a tester
tester
an individual organism homozygous for one or more recessive alleles
Mendel’s overall conclusions (5)
- difference btw yellow and green traits is that they carry a discrete and different hereditary determinant (mendel’s particulate factors)
- factors exist in pairs
- in each pair, one of the factors is dominant to the other (recessive and dominant alleles)
- parents pass one copy of each factor onto offspring; diploids produce haploid gametes, that have one cope of each gene, or one member of each homologous pair
- factors from parents unite independently of the type of factor; gametes fuse randomly
chromatid
one of the two side by side replicas produced by chromosome replication
sister chromatids
the juxtaposed pair of chromatids arising from the replication of a chromosome
homologous chromosomes
chromosomes that pair with each other during meiosis and (usually) have the same genetic loci (may have different alleles)
dyad
a pair of sister chromatids joined at the centromere
tetrad
four homologous chromatids in a bundle in the first meiotic prophase and metaphase
chiasma
a cross-shaped structure commonly observed btw non sister chromatids in meiosis
- the site of crossing over
s-phase
DNA molecules replicate to form identical chromatids
- making a copy of the existing DNA
molecular marker
a site of DNA heterozygosity (difference), not necessarily associated with phenotypic variation, used as a tag for a particular chromosomal locus
hemizygous gene
a gene that is present in only one copy in a diploid organism
reciprocal crosses
a pair of crosses of the type genotype A (female) x genotype B (male) and B (female) x A (male)
prophase
- chromatids coil and condense to become visible
- mitotic spindle forms outside of nucleus, consists of microtubules
- nuclear envelope breaks down and nucleoli disappear
- kinetochores form on each face of the centromere
kinetochore
multiprotein complex that binds to centromere
- site of attachment for microtubules
metaphase
- chromosomes align along the metaphase plate
anaphase
- centromeres and sister chromatids separate from chromosomes
telophase
- migration of chromosomes to the poles is complete
- nuclear envelope reforms
cytokinesis
cellular division takes place to form the 2 new daughter cells (genetically identical)
mitosis generates
cells identical to mother cell
interphase
G1, S, G2
M phase
- prophase
- metaphase
- anaphase
- telophase
meiosis generates
haploid cells from diploid
MI
align and separate homologous pairs
- reduced division
MII
separate sister chromatids
- equational division
prophase 1 (5 phases)
leptotene, zygotene, pachytene, diplotene, diakinesis
leptotene
chromosomes condense
- become visible
zygotene
pairing of homologues, crossing over
- synaptonemal complex begins to form
pachytene
synaptonemal complex complete (compressed)
diplotene
slight separation of synaptonemal complex to form chiasmata
diakinesis
further contraction of synaptonemal complex (compressed again)
synaptonemal complex is made of
DNA and protein
function of the synaptonemal complex
facilitates crossing over
metaphase 1
- homologs move to the equatorial plane
- centromeres attach to the spindle
- line up as tetrads
anaphase 1
- one homolog moves to each pole
- sister chromatids DO NOT separate
- separate homologous pairs (still dyads)
telophase 1
- migration complete
- nuclear membrane MAY reform
- cytokinesis MAY occur
prophase 2
condensed chromosomes
metaphase 2
dyads aligned along equatorial plane
anaphase 2
separation of centromeres and sister chromatids
- results in two chromosomes
telophase 2
nuclei reform
cytokinesis to produce 4 haploid daughter cells
sex-linked single-gene inheritance patterns
genes that show different phenotypic ratios
autosomal dominant pedigree
- trait appears in every generation
- affected parents have affected children
- no correlation between sex and a particular phenotype
x-linked recessive pedigree
- phenotype is more common in males than females
- affected fathers have no affected children - however, all daughters are carriers
- trait passed from grandfather to grandson
x-linked dominant pedigree
- fathers pass traits to all daughters - however, no sons are affected
2, mothers pass trait to half sons and daughters
y-linkage
no conclusive cases
1. phenotype passed from father to all sons - not to daughters
